In the field of electrical circuit breakers, it is well known to provide an external indication of the internal state of the circuit breaker, for example ON, OFF, and TRIPPED.
A circuit breaker is a device, which serves to interrupt electrical current flow in an electrical circuit path upon the occurrence of an overcurrent in the circuit path. When the overcurrent occurs, the external toggle handle will normally return to the OFF position. However, a service technician of other user will have no indication whether the breaker was intentionally turned OFF or the breaker tripped. In complex breaker installations, where some breakers are normally maintained in an OFF position, this can make analysis difficult. Therefore, the art has taught the desirability of an external indication of switch state.
Various methods are available for indicating Trip State of a breaker. First, the external toggle handle may be provided with a "mid-trip" state, intermediate from the ON and OFF states. This is typically accomplished by a linkage between the external toggle and trip mechanism, wherein, upon a trip condition of the breaker, the trip mechanism assumes a state, which causes the external toggle to lie in an intermediate state. See, e.g., U.S. Pat. No. 5,264,673, 4,528,531, 3,970,976, 3,955,162, and 3,863,042, expressly incorporated herein by reference. An electronic indicator may also be provided, for example, a light emitting diode, which is selectively illuminated by power from the load. See, e.g., U.S. Pat. No. 3,806,848, expressly incorporated herein by reference, or by means of an auxiliary switch, see, U.S. Pat. Nos. 3,742,402, 3,742,403, 3,863,042 and 3,955,162, expressly incorporated herein by reference. Some circuit breakers have an internal trip condition distinct from the OFF condition. See, e.g., U.S. Pat. No. 5,777,536. This latter solution, however, causes the problem that in the tripped condition, a small current still flows through the device. Other types of mechanical visual indicators are also possible.
The solution proposed in U.S. Pat. Nos. 3,955,162 and 3,863,042 provide a ramp surface of a flat spring, that is disposed within the path of a member extending from an internal portion of the handle. During each actuation of the circuit breaker, the flat spring is flexed, potentially resulting in stress-related failure of the spring. Since this spring is metallic, such failure poses a particular hazard of shorting the breaker. Further, it is often possible to "tease" the circuit breaker into the mid-trip state without an immediately antecedent trip event. The simple design is typically available only for smaller size circuit breakers, for example under 100 Amps rating, due to the inertia of the contact bar and handle, and the handle return spring of larger rating circuit breakers overcoming the retaining spring forces of the flat spring during a trip. Therefore, larger size breakers require damping of the handle movement by additional elements. Finally, in the design employing a flat spring, the handle assumes a mid-trip position even if the contacts are welded together, thus failing to warn service personnel that the protected circuit may be "live".